In a converter system, current detection is very important for realizing current mode control, current sharing, current monitoring, current overload limiting and current overload protection. The existing current detection method performs detecting/sampling to an output current by using a current detection resistor with high accuracy, by using a direct current (DC) resistance of an output conductor, or by using an on-resistance of switch, etc.
FIG. 1 is an existing current detection circuit using the current detection resistor with high accuracy. As shown in FIG. 1, the current detection resistor includes a sampling resistance Rsense and a differential amplifier OPA. An output inductor Lo has an inductance L and an equivalent series resistance DCR. The output inductor Lo is connected to the sampling resistance Rsense in series. Input terminals of the differential amplifier OPA are connected to the sampling resistance Rsense in parallel for amplifying a voltage signal across the sampling resistance Rsense so as to obtain a current detection signal. The magnitude of the current signal flowing through the sampling resistance Rsense may be known by measuring voltages across the sampling resistance Rsense and via I=V/R. It should be noted, the sampling resistance Rsense is a current detection resistor with high accuracy.
The method for detecting current by using a current detection resistor with high accuracy has the advantage of high current detection accuracy and low temperature drift. Since a resistance with a low temperature coefficient may be adopted, the influence by the temperature drift can be avoided. However, this method has the following deficiency: when the current flowing through the current detection resistor is relatively large, a relatively large loss may be occurred in the current detection resistor, thereby heat dissipation issues need to be considered during the design of circuit. In addition, the current detection resistor with high accuracy occupies a relatively large space.
FIG. 2 is an existing current detection circuit using the on-resistance of switch, which can efficiently save space and have a relatively low conduction loss. However, this solution has relatively low current detection accuracy and relatively large temperature drift.
FIG. 3 is an existing current detection circuit using a parasitic resistance of the output inductor. As shown in FIG. 3, the current detection circuit includes an output inductor Lo, a resistance R, a capacitance C and a differential amplifier OPA, wherein the output inductor Lo includes an inductance L and an equivalent series resistance DCR. The resistance R and the capacitance C constitute a RC filtering circuit for filtering sampling signals of the output inductor Lo.
When L/RDCR=RC is satisfied, a voltage on the capacitance is in proportion to a current iL flowing through the inductance L. Thereby, the magnitude of the load current and inductive current may be detected only by detecting the magnitude of the voltage on the capacitance. Such method is convenient and simple, can save space efficiently, and has a relatively low conduction loss, but has relatively low current detection accuracy and relatively large temperature drift.
Therefore, a new current detection solution is needed.
The information described above is only used to enhance the understanding of the background of the present disclosure, and thus may include the information which is not regarded as the ordinary skill in the art for the person skilled in the art.